This invention relates to a tunable antenna module and a manufacturing method thereof, in which the capacity of a variable capacity means connected to an antenna element is changed by the control voltage of a frequency control source, and a tuning frequency is changed according to the frequency of an electric wave received by the antenna element.
The digital terrestrial broadcasting is the television broadcasting performed by using a radio station of a ground digital method. It is scheduled to replace analog television broadcasting (VHF 1-12 ch) started in 1953 with a digital method in which only UHF channels (470-770 MHz band and 13-62 ch) will be used in July 2011 in Japan.
In the digital terrestrial broadcasting, a multi-channel OFDM (Orthogonal frequency division multiplex) method is used. Therefore, it is possible to make different digital modulation in each segment by dividing the career into 13 segments.
A usual television, a computer such as a desktop type computer and a notebook-sized personal computer can provide four channels for three segments. Moreover, 12 segments are used in a high definition broadcasting, and the remaining segment is used to broadcast one segment television (partially receiving service of one segment for a cellular phone or a mobile terminal for data transmission. The reception of one-segment television has aimed at use with mobile and portable equipment such as a cellular phone, car-navigating equipment, PDA (a personal digital assistance), and a game machine.
There is a monopole antenna or a conventional tunable antenna module 71 shown in FIG. 7 as an antenna which can receive such digital terrestrial broadcasting.
In tunable antenna module 71, variable capacitance diode (VCD) 73 is connected with wave receiving element 72. VCD is also called a varicap diode or a variable condenser. Capacitor 74 for cutting off a DC (direct current) is connected with VCD 73. Resistance 75 for cutting off an RF (radio frequency) is connected between for VCD 73 and DC cutting-off capacitor 74. Frequency control source 76 is connected with a power supply side terminal of resistance 75 for cutting off the radio frequency.
The capacity of VCD 73 is changed by a control voltage of frequency control source 76, and the tuning frequency is changed according to the frequency of the electric wave received by wave receiving element 72. Thereby, the broadcasting in the desired channel is received in this tunable antenna module 71.
The prior art which relates to the present invention is disclosed in the following documents.    (1) JP10-173426A (Tune type, especially FIG. 2).    (2) JP2000-151448A (Tune type)    (3) JP2003-298341A (Tune type, especially FIG. 3).    (4) JP2006-345042A (Microcomputer control type)